(a) Field of the Invention
The present invention relates to a fail-safe control method for an automatic transmission having a one-way clutch in which, when one-way clutch roll-over occurs, shifting is performed into a second speed from a first speed after a forced downshift operation into the first speed is effected, thereby carrying out a fail-safe operation.
(b) Description of the Related Art
A one-way clutch is typically provided at two locations: between a planet carrier of a planetary gearset and a center support in a sprag configuration or on a stator of a torque converter. The one-way clutch transmits power in only one direction.
Since a long pinion of the one-way clutch of the planetary gearset rotates clockwise when in a first speed of a drive D range or a low 2 range, the counterclockwise rotation of the planet carrier of the planetary gearset is impeded such that drive power is transmitted to a ring gear of the planetary gearset. Accordingly, the planet carrier is able to rotate only clockwise and free-wheels in a clockwise direction during engine braking such that shifting into the second speed from the first speed is performed smoothly.
However, in the case where the one-way clutch of the transmission undergoes roll-over, driving in the first speed is not possible and a situation results in which engine rpm abruptly increase. In conventional vehicles, although there are systems which alert the driver that a malfunction has occurred, no internal countermeasure is taken when such a problem arises.